Thermomechanical Treatment Of 2124 Aluminum Alloy Creep Aging

Creep age forming technique was mainly used for large aircraft panels, which took the advantage of the creep characteristics of the metal. During the creep aging process, aging and forming would be occured simultaneously and affected mutually. The pre-deformation, pre-aging, grain size, alloy composition and so on, would impact on the resilience and ultimate performance during creep age forming. In this paper, three different initial heat treated 2124 alloys (SHT- solution heattreatment, FTMT- pre-deformation+pre-aging, ITMT- grain refinement) were used for creep aging experiments, and then analysed by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and other tests. The effects of the initial states of the 2124 aluminum alloy on the creep age forming were investigated, several conclusions were obtained as follows:(1) ITMT refined the grains of 2124 aluminum alloy, which increased the grain boundaries and made increasing of the creep deformation. FTMT increased the dislocations and the movable dislocations within the alloy. The dominated creep mechanism of the FTMT alloy changed from dislocation climb mechanism to viscous sliding. Therefore the initial stage of creep deformation of the FTMT alloy decreased, but the steady-state creep rate increased.(2) The unified creep constitutive equations of 2124 aluminum alloy were obtained. Two different constitutive equations for three different initial condition alloys were fitted well.(3) The effects of creep aging on microstructures and mechanical properties of 2124 aluminum alloy were revealed. During the process of the creep aging,θ'phase exhibited the stress oriented effect, but the main precipitation strengthening phase-S' phase was not obvious, but the precipitates along the stress axis with thick phenomenon. Compare to the artificial aging, the prepititated particles were finer and more compact, and PFZ became narrower, but the anisotropy index of ductility and toughness were increased because of the narrowed PFZ. (4) The effects of ITMT on microstructures and mechanical properties of 2124 creep aging alloy were revealed. There were coarse insoluble Fe (Si)-rich particles in solid solution-hot rolling alloy and ITMT alloy, which were broken during aging for the creep stress, the greater the creep stress the more serious. ITMT can obtain fine grains, which made the alloy had good strength and plasticity, but also good mechanical properties remain after creep aging.(5) The effect of FTMT on microstructure and mechanical properties of 2124 creep aging alloy were revealed. A appropriate FTMT technology was natural aging for 12h+ pre-deformation by 8% percent, which can obtain good mechanical properties after aging creep. FTMT pretreatment can eliminate the stress oriented effect, refined the second phase, improved the alloy strength and reduced the change of the plasticity and toughness of anisotropic index, but ductility and toughness decreased slightly.